The present invention relates to fluid loss control operations. More particularly, the present invention provides compositions comprising ceramic particulate bridging agents and improved fluid loss control additives, and methods of using those compositions to provide fluid loss control.
Drilling and servicing fluids, inter alia, deposit filter cake on the walls of well bores within the producing formations to substantially prevent drilling, servicing, and completion fluids from being lost into the formation and solids from entering into the porosities of the formation. After the drilling or servicing operation has been completed, the filter cake is removed prior to placing the formation on production. Removal of the filter cake heretofore has been accomplished by including a water, oil, or acid soluble particulate solid bridging agent in the treatment fluid for bridging over the formation pores or other opening. Such areas include formation pore throats, gravel packs, sand screens, or fractures in the formation as well as openings such as cracks in tubing or casing, holes in sand screens, or on other perforations downhole such as in a shroud, casing, or other tubing. By bridging across such areas, the bridging agents combined with a fluid loss control additive form a substantially impermeable “filter cake” on that area that prevents loss of treatment fluids to the surrounding formation.
Common bridging agents include calcium carbonate, suspended salts, or oil-soluble reins. For lost-circulation treatments outside the production interval, any suitably sized product may be used, including mica, nutshells, and fibers. The selection of an appropriate bridging material is more critical in the production interval and during work-over operations since the barrier should be completely removed in preparation for placing the well back into production. As an alternative to conventional bridging agents, chemically bonded ceramic particulates are desirable because they are customizable as these particulates are made via a process similar to that of mixing a cementitious material. As a result, their composition, and properties can be varied, and they can be impregnated with desirable additives. Another advantageous feature of these particular bridging agents is that they are soluble in ammonium salts and chelating agents.
Starches are often used in conjunction with bridging agents, inter alia, to aid in the prevention of fluid loss to the formation. Starches are carbohydrates of a general formula (C6H10O5)n, and are derived from corn, wheat, oats, rice, potatoes, yucca, and the like. Most starches usually comprise about 27% linear polymer (amylose) and about 73% branched polymer (amylopectin). These two polymers are intertwined within starch granules. Granules generally are insoluble in cold water, but soaking in hot water or under steam pressure ruptures their covering and the polymers hydrate into a colloidal suspension. Amylose and amylopectin are nonionic polymers that do not interact with electrolytes. Derivatized starches, such as hydroxy propyl and carboxylmethyl starches are used in drill-in fluids, completion fluids, and various brine systems as well as in drilling fluid systems.
Problems arise, however, when conventional starches are added to fluids comprising chemically bonded ceramic particulates. When combined, the fluid gels to a point where it ultimately has the consistency of paste. As a result, this combination is unusable in downhole applications. This is unfortunate because the starch provides an added means to ensure fluid loss control in a process using the desirable chemically bonded ceramic particulates.